There is one inside the \Windows\Driver Cache\i386 folder.
If you have installed one of those Windows updates that replace the kernel, it is directly in this folder.
The command at the recovery console would be
copy "C:\Windows\Driver Cache\i386\ntoskrnl.exe" C:\Windows\system32

If you haven't applied one of these updates but have Service Pack 1 installed the ntoskrnl.exe is inside the sp1.cab file.
The command in this case
expand "C:\Windows\Driver Cache\i386\sp1.cab" /f:ntoskrnl.exe C:\Windows\system32

In case you don't even have SP1 installed, replace sp1.cab in the command by driver.cab.